The present invention relates to an X-ray television apparatus and, more particularly, to a structure for coupling an X-ray image intensifier with an imaging unit.
X-ray television apparatuses are now widely employed in such fields as medicine and industry. Typically X-rays are generated by an X-ray generator and transmitted through a subject/object under examination, with the resultant X-ray image being incident on the input phosphor screen of the X-ray image intensifier incorporated in the X-ray television apparatus, where it is converted into a visible image, and this visible image is converted into photoelectrons by a photoelectric surface. These photoelectrons are focused and accelerated by electrodes to form an electron image on an output phosphor screen of the X-ray image intensifier, and this electron image is converted into a visible image by the output phosphor screen. The visible image from the X-ray image intensifier is transmitted to a photoconductive film of an imaging unit and is converted into an electrical signal. Conventionally, this visible image is transmitted from the X-ray image intensifier to the imaging unit as follows. That is, an optical lens system or an optical fiber optical system is known as transmitting means. In an apparatus adopting an optical lens system, the visible image from the output phosphor screen of the X-ray image intensifier is transmitted through a tandem lens system as the optical lens system and is imaged on the photoconductive film of the imaging unit. In an apparatus adopting the optical fiber optical system, as described in U.S. Pat. Nos. 3,058,021 and 3,967,123, the visible image is directly incident on an optical fiber bundle, transmitted therethrough, and then imaged on the photoconductive film of the imaging unit. The optical fiber optical system has better light transmission efficiency than that of the optical lens system. Therefore, the X-ray television apparatus having the optical fiber optical system does not have a lens and hence can be advantageously made compact in size. However, in the X-ray television apparatus having the optical fiber optical system, a visible image output end face of an optical fiber bundle connected to the output phosphor screen of the X-ray image intensifier must be optically coupled with accuracy and reliability to a visible image input end face of an optical fiber bundle connected to the photoconductive film of the imaging unit. As such an optical coupling structure for satisfying the above requirement, a diaphragm structure is described in U.S. Pat. No. 3,967,123. This diaphragm structure is a disk which has a central open portion and a plurality of lugs extending spirally from a ring portion toward the center. Tips of the lugs are engaged with a rim of the imaging unit, and the X-ray image intensifier is coupled to the imaging unit by an elastic pressure of the diaphragm, thereby optically coupling the two optical fibers. However, a structure of couple means using the diaphragm having the lugs poses the following problems. That is, in this structure, since the elastic pressure of the plate-like diaphragm changes quadratically with respect to a displacement amount, it is difficult to set the elastic pressure. In addition, since the diaphragm has gaps between the lugs, an electric field generated from a portion near an output section of the X-ray image intensifier enters into the imaging unit as electrical noise, thereby generating a pseudo signal as noise from the photoconductive film of the imaging unit. This pseudo signal degrades an S/N ratio of the imaging unit and hence degrades frequency characteristics of the X-ray television apparatus. Furthermore, since the elastic pressure is applied on the rim of the imaging unit by the lug tips of the diaphragm engaged therewith, a load is concentrated onto an engaged portion and the rim tends to be distorted. As a result, a vacuum seal capacity of the imaging unit and transmission efficiency of an output signal may be degraded. Moreover, since the tips of the lugs are brought into contact with the rim of the imaging unit by the elastic pressure of the diaphragm, perfect surface contact cannot be obtained. As a result, an optical axis of the optical fiber at the side of the X-ray image intensifier is largely deviated from that of the optical fiber at the side of the imaging unit.